text: Nitrile ylides also known as nitrilium ylides or nitrilium methylides, are generally reactive intermediates formally consisting of a carbanion of an alkyl or similar group bonded to the nitrogen atom of a cyanide unit. With a few exceptions, they cannot be isolated. However, a structure has been determined on a particularly stable nitrile ylide by X-ray crystallography. Another nitrile ylide has been captured under cryogenic conditions. 
  As ylides, they possess a negative charge and a positive charge on adjacent atoms. However, they also have resonance, including 1,3-dipole contributing structures: 
  The most appropriate resonance structure is dependent upon the substituent pattern (the identity of the R and R′ groups).  The 3-dimensional structure of the nitrilium ylide itself may also provide a clue as to the most appropriate resonance structure, with a linear R–C≡N–C unit supportive of the charge distribution indicated for resonance structures 1a & 1b and also consistent with the nomenclature nitrilium ylide.  As resonance structures 1c and 1d become more important the nitrilium ylide distorts its geometry from linear in favor of a different valence tautomer 2 that is distinctly bent:
  Nitrile ylides are isoelectronic with nitrile oxides: